Definition
A hardened steel washer made from a single coil of square or rectangular cross-section that has been split and slightly spread, so the two ends sit at different heights. When compressed under a nut or bolt head, the sharp ends bite into the mating surfaces and the spring tension of the coil resists loosening from vibration.
Plain English
A small metal ring with a gap in it, twisted slightly so one end sits higher than the other. When you tighten a bolt down on it, it flattens and presses back, helping to stop the bolt from shaking loose.
Context Anchor
Seen in aircraft maintenance, especially when checking or installing hardware on panels, brackets, accessories, and other parts that are held by nuts, bolts, or screws.
Derivation
Split' refers to the gap cut through the ring; 'lock' describes its job of resisting loosening; 'washer' is the general term for a flat ring placed under a fastener. The name describes exactly what it does.
Why Pilots Care
Vibration in flight can loosen fasteners; the washer maintains torque and prevents loss of structural integrity or control function.
Intuition Check
“Lock” does not mean it permanently locks the nut or screw in place. It only helps resist loosening by adding spring pressure; correct installation and approved hardware are still required.
Example Sentence 1
The mechanic installed a split lock washer under each nut to help keep the inspection panel screws from backing out in flight.
Example Sentence 2
During the preflight walk-around, the pilot checked that all visible split lock washers on the control linkages remained compressed.